Multiple-Input-Multiple-Output (MIMO) communication systems use multiple antennas at a transmitter and receiver, for the transmission and reception of multiple “streams.” MIMO promises significant increases in throughput, but comes at the expense of increased processing complexity at the transmitter and at the receiver. As an example, the 3rd Generation Partnership Project (3GPP) is developing LTE as a fourth-generation wireless communication standard, and that development relies heavily on the use of various MIMO technologies, including transmit diversity, single-user (SU) MIMO supporting up to four spatial multiplexing layers for signal transmission/reception, and multi-user (MU) MIMO, which allows for the allocation of different spatial layers to different users.
In particular, receiver processing complexity can increase significantly, given the need to separate the received MIMO streams, at least to the extent necessary for recovering those streams of interest. For example, Maximum Likelihood Detection (MLD) may be used for multi-stream processing, but such ML-based detection often imposes significant processing and memory requirements on the receiver.
There are lower-complexity alternatives, such as described in U.S. patent application Ser. No. 12/549,132, as filed on 27 Aug. 2009, and in U.S. patent application Ser. No. 12/549,157 (filed on the same day). Those applications provide example details and explanations for a type of multi-stage detector that advantageously uses joint processing for recovering multiple MIMO streams. In particular, these applications describe a “SLIC” receiver structure.
The acronym stands for Serial Localization with Indecision and Color whitening, and SLIC receivers use a multi-stage structure. The indecision feature of SLI derives from the key ingredient of representing the modulation constellation with overlapping subsets. Correspondingly, each SLIC stage includes a joint demodulation (JD) unit capable of handling a subset of the received MIMO streams simultaneously. The remaining streams are treated as colored noise, and suppressed with a pre-filter.
Of course, SLIC receivers are just one example where subsets of MIMO streams are jointly processed, as part of received signal processing. It is advantageously recognized herein that, in SLIC and other contexts, receiver performance is significantly affected by the partitions used to form the subsets of MIMO streams used in joint processing, and overall performance can thereby be improved through better subset selection.